1. Field of the Invention
This invention relates generally to an apparatus and method for determining position information. More particularly, this invention relates to a receiver unit that receives direction and timing information and, using the received information, can be used to determine azimuth and elevation of an object or point within an area.
2. Description of the Related Art
Precise position measurement data is necessary or useful in a variety of technical fields. Obvious examples include navigation for airplanes and ships which in light of recent technical advances often include navigational aides utilizing global positioning system (GPS) data that may be overlaid on maps to facilitate navigation. The precision of GPS, however, is limited to within a few meters due to the granularity of the satellite sensors and the errors that build up over the long distances. Three dimensional position information and data is likewise useful in many other industrial arts including robotic control, virtual reality, augmented reality and particularly the building and construction trades.
Three-dimensional positional information gathering apparatus and systems are often costly to deploy in construction type environments and often require highly skilled operators to install and operate the equipment. For example, multiple transmitters might require multiple line of sights and other setup criteria that can only be obtained using large and expensive equipment which is often not well adapted to field use. One example is a low cost precision three-dimensional system described in the U.S. patent applications identified above. These user friendly precision three-dimensional measurement systems employ at least two optical transmitters, one or more selectively positional optical receivers and sophisticated algorithms for calculating three-dimensional data within the predetermined work area.
As will be well recognized by those skilled in the construction and building trades, many commercially significant tasks require precise position measurement information or data. For example, in land surveying it is known to measure the height, distance and angular position with respect to a known reference point using three separate instruments.
Three-dimensional data is generally not required for most building and construction uses. For example, leveling a floor in the building trade requires only a horizontal plane which is only-one value of elevation (elevation equal to zero). Turning an angle from a corner location to mark the position of a wall requires a vertical plane rotating about an axis, only one dimension in this case azimuth. Laying out a dual slope requires azimuth and elevation data, totaling two dimensions. Similarly, a myriad of other such applications in the building and construction trades can be performed with combinations of elevation and azimuth data relating to a particular task. Thus a precise position measurement system that provides two-dimensional data would have many practical commercial building and construction applications. However, as with the three-dimensional position measurement systems, two-dimensional position measurement systems in the past have not been adapted for efficient field use. Additionally, prior art two-dimensional measurement systems generally required two or more operators and were difficult to set up and maintain for field operation.
U.S. Pat. No. 4,441,809 to Dudley et al. teaches the taking of all three surveying measurements, the height, the distance, and the angular position, by a single operator using a two-part instrument: a beam transmitter and a receiver. The receiver unit requires two sensors spaced a known distance apart in a direction parallel to the axis of rotation of a transmitted beam. In this manner, when a V-beam is transmitted about a vertical axis to define a horizontal reference plane, the sensors are vertically spaced. The distance between the leading and trailing edges of the beam is greater at the upper sensor than at the lower sensor. If a measure of these distances is made, the distance of either sensor from the horizontal reference plane and their distance from the axis of rotation can be calculated. However, the transmitter sends a corresponding RF signal carrying a digital signal containing the rotational information related to the angular position of the beam. This RF signal is received by the receiver and supplied to a circuit that contains pulse counters. Light sensors provide start and stop times as the laser beam sweeps for use by the counters. An opaque mask having apertures matching the beam inclination and orientation is placed in front of the light sensor. This allows only predetermined beam portions corresponding to sharp pulses to be detected and sent to the pulse counters. In this manner, Dudley ""809 requires 1. that the receiver must be level in order for the beams to proceed through the mask apertures, 2. at least two sensors spaced apart in the vertical plane, 3. encoders for counting the received signals, and 4. a separate RF signal receiver for receiving RF pulse signals from the transmitter.
Thus there is a need for a low cost spatial positioning system capable of generating precise two-dimensional information and which is well adapted to efficient field setup and use, including not requiring two spaced apart sensors, does not require a separate RF receiver for receiving RF pulse signals from the transmitter, and does not require an opaque mask.
It is an object of the present invention to provide a low cost two-dimensional position measurement apparatus and process which is both easy to set up in the field and capable of single operator utilization.
It is another object of the present invention to provide a two-dimensional measurement apparatus and process which is precise, rugged, reliable and easy to set up and used by a single operator under construction site conditions.
It is another object of the present invention to provide a receiver having a single optical sensor for use in a robotic theodolite system.
It is another object if the present invention to provide a receiver having a single optical sensor that can compute at least one of azimuth and elevation relative to a transmitted optical signal.
It is a further object of the present invention to provide an improved low cost robotic theodolite system and procedure for conveniently generating azimuth and elevation angle data based upon detected timing differences between illuminating laser beam strikes and a reference strobe and based upon convenient calibration data for the utilized optical transmitter.
Novel features of applicants"" invention are directed to overcoming the above described deficiency in prior art precision position measurement systems by providing a novel receiver apparatus and processes for: (i) calculating elevation angles based upon laser fan beam strikes or hits from a single rotatably mounted transmitter that emits two constant laser beams from a rotating head, where selected parameters of the rotating fan beams have been determined during a calibration procedure associated with the manufacture of said transmitter, and a receiver which uses a single light responsive element, (ii) further calculating azimuth angles using a single periodic reference pulse from a series of light emitting diodes, (LEDs) the reference pulse preferably generated once per revolution of the transmitter rotating head and the reference pulse being received by the same single light responsive element. In another embodiment of the present invention the improved system and process can be adapted to make distance calculations by using two receivers, which are positioned in the measurement field at a known distance separation, and which receive only the two rotating laser beams and the reference pulse.
In the apparatus and method of the present invention, following setup of the transmitter, a single user transports the receiver to a desired location, points the receiver in the general location of the transmitter, and from a user readable display on the receiver is informed of the desired parameters of the location. The desired parameters can be one of many parameters derived from the receiving of the transmitted optical beams, including azimuth, elevation, and distance from the transmitter.
User interaction with the receiver is another important feature of the apparatus. For example, a display screen on the receiver can indicate to the user a direction to move the receiver in order to arrive at a predetermined location. Alternatively, the user can input into the receiver the desired location, and the receiver, upon receiving the transmitted beams, indicates to the user which direction to move the receiver within up to six degrees of freedom, that is, up, down, left, right, forwards and backwards in order to approach and arrive at the desired location.
In the preferred embodiment of the receiver, a single broadband wide-angle detector is used to detect the two transmitted optical beams and the periodically transmitted strobe.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.